1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to multi-piece golf balls having a center, a mid layer, an inner cover and an outer cover.
2. Description of the Related Art
Golf players' greatest demand for golf balls is flight performance. Golf players emphasize flight performance with a driver, a long iron and a middle iron. The flight performance is correlated with the resilience performance of the golf ball. When the golf ball excellent in resilience performance is hit, the golf ball flies at a fast speed to accomplish great flight distance. The flight performance is further correlated with spin rate. The golf ball flies at a small spin rate, thereby obtaining proper trajectory to accomplish great flight distance. In light of flight performance, golf balls which have high resilience performance and are not likely to be spun are desired. Golf players further emphasize feel at impact. Golf players prefer soft feel at impact.
Japanese Unexamined Patent Application Publication No. 8-336617 (U.S. Pat. No. 5,688,569) discloses a golf ball having a core, an inner cover and an outer cover. This core has a two-layered structure. The outer cover is soft.
Japanese Unexamined Patent Application Publication No. 9-56848 (U.S. Pat. No. 5,725,442) discloses a golf ball having a core, an inner cover and an outer cover. This core has a two-layered structure. The inner cover includes polyester as a principal component, while the outer cover includes an ionomer resin as a principal component.
Japanese Unexamined Patent Application Publication No. 9-266959 (U.S. Pat. No. 5,743,816) discloses a golf ball having a core and a cover. This core has a three-layered structure. Each layer of the core is made of rubber composition.
Japanese Unexamined Patent Application Publication No. 2001-29510 (U.S. Pat. No. 6,461,251) discloses a golf ball having a core, a mid layer and a cover. This core includes an inner layer and an outer layer. The outer layer is hard.
Japanese Unexamined Patent Application Publication No. 2002-272880 (US2001/0024982) discloses a golf ball having a core and a cover. This core comprises a center and an outer core layer. The cover comprises an inner cover layer and an outer cover layer. The outer cover layer is soft.
Japanese Unexamined Patent Application Publication No. 2004-130072 (US2004/029648) discloses a golf ball having a core and a cover. This core comprises a center, a mid layer and an outer layer. The cover includes polyurethane elastomer as a principal component.
Japanese Unexamined Patent Application Publication No. 2005-152397 discloses a golf ball having a core, a mid layer and a cover. This core comprises an inner layer and an outer layer. The compression of a spherical body including the core and the mid layer is smaller than the compression of the inner layer.
Japanese Unexamined Patent Application Publication No. 2006-230661 discloses a golf ball having a core, a mid layer and a cover. This core has a two-layered structure. The core includes an inner layer and an outer layer. The inner layer is hard.
When a golf ball has an outer-hard/inner-soft structure, the spin may be suppressed. The conventional golf ball uses a soft center, a hard mid layer and a hard cover in order to attain an outer-hard/inner-soft structure. In this golf ball, the hardness distribution up to the central point of a center from the surface of a mid layer has a large level difference on the boundary of the center and the mid layer. This level difference deteriorates the suppression of spin. A soft center deteriorates the resilience performance. Further, a hard cover deteriorates feel at impact.
Golf players' demand to the golf ball has been increasingly escalating. It is an object of the present invention to provide a golf ball having excellent flight performance and excellent feel at impact.